Critical Opalescence in Carbon Dioxide

One feature of the teaching at Dalhousie University’s Physics Department is a laudable emphasis on demonstrations.

Visiting Professor Tom Duck there, I was delighted to be shown a demonstration I had heard of, but never seen: the phenomenon of critical opalescence in carbon dioxide.

I have written about critical opalescence previously on this blog (here) and with more pictures (here), so I won’t repeat most of that.

In my previous articles I described the phenomenon in two immiscible liquids which is an exact analogy for the physics of critical opalescence in a pure substance. But it’s not what physics students read about in text books.

Michael: What are you going on about?

The phenomenon occurs when one heats a liquid in a container with a small amount of free space.